Apparatus and method for OFDM data communications

ABSTRACT

A radio system employing Orthogonal Frequency Division Multiplexed (OFDM) includes a Base Transceiver Station (BTS) along with a number of mobile terminals located within a coverage area of the BTS. In this system, a target mobile terminal is provided with a focused transmission beam to receive high data rate traffic information while the remainder of the mobile terminals are provided with pilot and signalling information. To achieve both objectives, a BTS is implemented with a transmission apparatus that generates a directional transmission beam for the data traffic information. In one design, this directional beam transmits the pilot and signalling information along with the data traffic information by rotating the beam within the coverage area. In another design, the BTS has a transmission apparatus that generates more than one transmission beam. In one case, the BTS transmits a directional transmission beam for the data traffic information required by the target mobile terminal and a second broad transmission beam for the pilot and signalling information required by the all of the mobile terminals. In another case, the BTS transmits two directional transmissions beams, one beam for data traffic information and one rotating beam for pilot and signalling information.

RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.09/842,128 filed on Apr. 26, 2001 and claims the benefit of U.S.provisional application Ser. No. 60/258,558 filed on Dec. 29, 2000.

FIELD OF THE INVENTION

This invention relates generally to radio data communications and, inparticular, to apparatus and methods for Orthogonal Frequency DivisionMultiplexed (OFDM) data communications.

BACKGROUND OF THE INVENTION

In an OFDM system, a Radio Frequency (RF) channel (or bearer) that istransmitted from a Base Transceiver Station (BTS) to one or more mobileterminals is subdivided into a plurality of data traffic carriers withoverlapping spectrum along with various pilot and common signallingcarriers that are distributed across the RF channel. The pilot carrierswithin an RF channel are utilized to broadcast pilot information, whichis generally referred to as a pilot channel, from a Base TransceiverStation (BTS) to one or more mobile terminals, this pilot channel beingused by the mobile terminals for frequency reference, carrier recoveryand channel estimates. The signalling carriers within an RF channel areutilized to communicate signalling information (such as controlmessages), which is generally referred to as signalling channels, fromthe BTS to mobile terminals. The data traffic carriers within an RFchannel are utilized to communicate data traffic information, generallyreferred to as data traffic channels, from the BTS to mobile terminals.

In an OFDM system, there is a need for the pilot information andsignalling messages to be consistently transmitted to all mobileterminals in a particular coverage area. In a well-known implementation,the pilot, signalling and data traffic channels for a given RF channelshare the same antenna beam which is transmitted to an entire coveragearea from the BTS, the coverage area generally being a single sectorwithin a sectorized wireless network. In this implementation, a sectoromni-directional antenna is used that allows the pilot, signalling, anddata traffic channels to reach each mobile terminal within the coveragearea simultaneously. The coverage area may be the full 360 degree cellarea around the BTS or the coverage area may be a sector of the 360degrees. Commonly the cells are tri-sectored with each sector being 120degrees. The sector omni-directional antenna thus is designed to providecoverage throughout the sector and a number of sector antennas arearranged for full coverage of the cell. The pilot and signallingchannels are utilized by all of the mobile terminals within the coveragearea while the data traffic channels are processed only by the mobileterminal(s) that the data traffic was targeted for, these mobileterminal(s) being referred hereinafter as the target mobile terminals.

One problem with this implementation is the limited power (or link gain)that a sector omni-directional broadcast is capable of while reachingall of the mobile terminals within the coverage area simultaneously. Atthe high bit rates that the data traffic is typically transmitted at,the power to transmit the RF channel to the target mobile terminal(s)with a sector omni-directional broadcast would be relatively expensiveand possibly impractical. This is especially true, in cases wherephysical barriers such as walls and buildings are between the BTS andthe target mobile terminal(s). The use of a sector omni-directionalbroadcast further introduces the possibility of interference intoadjacent cells or sectors, this interference increasing as the power ofthe transmission increases.

Hence, modified transmission techniques are required that allow forsufficient signal power such that the BTS can reach any target mobileterminal within its coverage area. Preferably, this modifiedtransmission technique would also reduce the interference introducedinto adjacent cells or sectors.

SUMMARY OF THE INVENTION

The present invention is directed to apparatus and method for OFDM datacommunications. In the present invention, a BTS utilizes a directionalbeam to transmit data traffic channels to target mobile terminal(s). Inone embodiment, the directional beam contains the entire RF channel androtates through the coverage area such that each mobile terminal withinthe coverage area can have access to the pilot and signalling channelswhile the target mobile terminal(s) can have access to the entire RFchannel. In other embodiments of the present invention, the RF channelis divided into at least two beams, at least one beam transmitting thedata traffic channels, hereinafter referred to as the data trafficinformation, and at least one beam transmitting the pilot and signallingchannels, hereinafter referred to as the service information. Thisservice information may also include other kinds of information that ismeant to be broadcast to all mobile terminals within the coverage area.The beam transmitting the data traffic information is a directional beamto ensure sufficient power is directed at the target mobile terminal(s)while the beam transmitting the service information can either be asector omni-directional beam or a rotating directional beam.

The data traffic information may also include pilot carriers for thepurpose of channel estimation, synchronization and/or frequencyreference. It should be noted that when data traffic information isreferred hereinafter, it implies that it may include the pilot channels.If multiple beams are carrying the pilot channels using the samefrequency carriers and covering the same target mobile terminal, thentechniques such as coding may be used to differentiate the pilotcarriers belonging to the different beams.

The directional beam may be directed towards the target mobileterminal(s) by means of the mobile terminal(s) known location in thecase of fixed terminals. Alternatively, each of the target mobileterminal(s) could have locating equipment that allows it to report itslocation to the BTS or could be located with the use of feedbackinformation signalling sent from each of the target mobile terminal(s)to the BTS which is used by the BTS to direct the directional beam.

The present invention, according to a first broad aspect, is an OFDM BTSarranged to communicate with a plurality of mobile terminals within acoverage area including at least one target mobile terminal. In thisaspect, the BTS includes a processing apparatus and a transmissionapparatus. The processing apparatus operates to receive and processservice and data traffic information. The transmission apparatusoperates to receive the processed service and data traffic information,to transmit the processed service information on a first set of carriersto the mobile terminals within the coverage area with a firsttransmission beam and to transmit the processed data traffic informationon a second set of carriers to the target mobile terminal with a secondtransmission beam. In this aspect, the second transmission beam is adirectional transmission beam.

In one embodiment, the first transmission beam is sufficiently broad foreach of the mobile terminals within the coverage area to receive theprocessed service information. In another embodiment, the firsttransmission beam is a directional transmission beam. In this case, theBTS is operable to modify the direction of focus of the directionalfirst transmission beam in order for each of the mobile terminals withinthe coverage area to receive the processed service information.

In cases of directional beams being utilized, a number of embodiments oftransmission apparatus are possible. In one implementation, thetransmission apparatus includes a number of output paths, each of theoutput paths consisting of a phase adjuster coupled to the processingapparatus and further coupled in series with a transmitter and anantenna. In this case, the output paths each receive the requiredprocessed information from the processing apparatus and operate togetherto generate the directional beam by selectively adjusting theirrespective phase adjusters. In another embodiment, the transmissionapparatus includes a switch coupled to the processing apparatus and anumber of output paths coupled to the switch, each of the output pathsconsisting of a transmitter coupled to the switch and a directionalantenna coupled to its corresponding transmitter. In this case, theswitch receives the processed information from the processing apparatusand selectively forwards the processed information to a set of theoutput paths to generate the directional beam. In yet anotherembodiment, the transmission apparatus includes a single transmittercoupled to the processing apparatus, a switch coupled to the transmitterand a plurality of directional antennas coupled to the switch. In thiscase, the transmitter receives the processed information from theprocessing apparatus and processes this information in order to prep itfor transmission. The switch then selectively forwards the output fromthe transmitter to a set of the antennas to generate the directionalbeam.

In a second broad aspect, the present invention is an OFDM BTS similarto that of the first broad aspect but with a modified transmissionapparatus. In this aspect, the transmission apparatus operates toreceive the processed service and data traffic information, to transmitthe processed service information on a first set of carriers and theprocessed data traffic information on a second set of carriers using adirectional transmission beam. In this case, the BTS is operable tomodify the direction of focus of the directional transmission beam inorder for each of the mobile terminals within the coverage area toreceive the processed service information.

In a third broad aspect, the present invention is a Base TransceiverStation (BTS) arranged to communicate with a plurality of mobileterminals within a coverage area. In this aspect, the BTS includes meansfor receiving service and data traffic information, means fortransmitting the service information on a first set of carriers to themobile terminals within the coverage area and means for transmitting thedata traffic information with high link gain on a second set of carriersto the target mobile terminal.

In further aspects of the present invention are methods of transmittingservice and data traffic information to a plurality of mobile terminalswithin a coverage area, at least one of the mobile terminals being atarget mobile terminal. In one aspect, the method includes receivingservice and data traffic information, transmitting the serviceinformation on a first set of carriers to the mobile terminals withinthe coverage area with a first transmission beam and transmitting thedata traffic information on a second set of carriers to the targetmobile terminal with a second transmission beam, the second transmissionbeam being a directional transmission beam. In another aspect, themethod includes receiving service and data traffic information,transmitting the service information on a first set of carriers to themobile terminals within the coverage area with a directionaltransmission beam and transmitting the data traffic information on asecond set of carriers to the target mobile terminal with thedirectional transmission beam. In this aspect, the method furtherincludes modifying the direction of focus of the directionaltransmission beam in order for each of the mobile terminals within thecoverage area to receive the processed service information.

In yet another aspect, the present invention is a system including aBase Transceiver Station (BTS) according to one of the first and secondaspects and a plurality of mobile terminals within a coverage area ofthe BTS. In this case, at least one of the mobile terminals is a targetmobile terminal.

In an even further aspect, the present invention is a mobile terminalarranged to communicate with a BTS. In this aspect, the mobile terminalincludes a radio reception apparatus and a monitor apparatus coupled tothe radio reception apparatus. The radio reception apparatus operates toreceive and process service information on a first set of carriers fromat least one first transmission beam and to receive and process datatraffic information on a second set of carriers from at least one secondtransmission beam. The monitor apparatus operates to determine if one ormore of service information and data traffic information has beenreceived at the radio reception apparatus. If only service informationhas been received, the monitor apparatus operates to instruct the BTS toattend to the received service information. If only data trafficinformation has been received, the monitor apparatus operates toinstruct the BTS to attend to the received data traffic information. Andif service and data traffic information has been received, the monitorapparatus operates to instruct the BTS to attend to both the receivedservice and data traffic information.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described with reference to thefollowing figures, in which:

FIG. 1 is a block diagram illustrating a radio system using OFDM with arotating directional beam;

FIGS. 2A and 2B are block diagrams illustrating first and secondimplementations of the BTS of FIG. 1;

FIG. 3 is a chart illustrating pilot and signalling channels changingfrequency over time within an RF channel;

FIGS. 4A, 4B and 4C are charts illustrating a sample OFDM signal, thesample OFDM signal with the data traffic channels removed and the sampleOFDM signal with the pilot and signalling channels removed respectively;

FIG. 5 is a block diagram illustrating a radio system using OFDM with adirectional data traffic beam and a sector omni-directional servicebeam;

FIGS. 6A, 6B and 6C are block diagrams illustrating first, second andthird implementations of the BTS of FIG. 5;

FIG. 7 is a block diagram illustrating a radio system using OFDM with adirectional data traffic beam and a rotating directional service beam;

FIGS. 8A, 8B and 8C are block diagrams illustrating first, second andthird implementations of the BTS of FIG. 7;

FIG. 9 is a block diagram illustrating a radio system using OFDM inwhich two adjacent sectors each have a rotating directional beam; and

FIG. 10 is a block diagram of a mobile terminal that could be utilizedwithin the OFDM radio systems illustrated in FIGS. 1, 5 or 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of the present invention are directed to apparatus andmethods for Orthogonal Frequency Division Multiplexed (OFDM) radio datacommunications. In these embodiments of the present invention, at leastone directional beam, as will be described herein below, is utilized toensure data traffic channels being directed at a target mobile terminalhave sufficient power. As described below, there are numerous possibleimplementations for OFDM radio systems utilizing at least onedirectional beam for the data traffic channels.

Within the embodiments of the present invention described below, thecoverage areas for particular BTS comprise individual sectors, thoughthis should not limit the scope of the present invention. For highfrequency reuse, a wireless cell can be divided into n sectors, ncommonly being three within many current wireless implementations.Within a sectorized system, each sector is operationally treated as adifferent cell. It should be understood that in alternative embodiments,the present invention could be implemented within a coverage area otherthan an individual sector, such as an entire cell or another region ofspace.

Directional wireless beams, using multiple antennas which are sometimesreferred to as smart antennas, have been utilized previously withinwireless systems. Smart antenna technology includes intelligentantennas, phased arrays, Spatial Division Multiplex Access (SPMA)arrays, digital beam forming arrays, adaptive antenna systems andswitched beam antennas. In general, smart antenna technology can becategorized into two main groups: switched beam and adaptive arraytechnologies. Switched beam antenna systems form multiple fixed beamswith enhanced sensitivity in certain directions. This antenna system inoperation switches from one beam to another as needed to move thedirectional beam to the currently necessary direction. Adaptive antennatechnology, on the other hand, uses signal processing capabilities tolocate and track various types of signals in order to dynamically directa beam towards the mobile terminal to minimize interference and maximizeintended signal reception.

In a first embodiment of the present invention, as illustrated in FIG.1, a BTS 50 utilizes a directional wireless beam 52 to transmit datatraffic channels to a target mobile terminal 54. Data trafficinformation (within the data traffic channels), as stated above, mayinclude pilot signal information which may be used for channelestimation. The use of a directional beam system allows sufficient linkgain to transmit the data traffic channels within the RF channel to thetarget mobile terminal 54 by steering energy towards the terminal 54 andthus, improving radio link performance. The use of this directionalwireless beam achieves the needed power gain to the target mobileterminal 54 as well as reducing interference due to reuse of the same RFchannel in neighbouring cells (or even within the same cell). Directingthe energy in this way results in other mobile terminals 56 outside ofthe beam 52 to receive no or very limited amounts of the transmittedsignals within the RF channel. Thus, the mobile terminals 56 outside ofthe beam 52 cannot receive any broadcast pilot information or signallingmessages within the pilot and signalling channels.

To allow for the directional beam 52 to be used to transmit data trafficchannels to the target mobile terminal 54 while still allowing pilot andsignalling channels to be transmitted to all of the other mobileterminals 56 within the coverage area, a time division approach isimplemented in the first implementation illustrated in FIG. 1. In thisimplementation, the BTS 50 transmits the directional wireless beam 52 ina rotating fashion, hereinafter referred to as a rotating beam, for theRF channel. In this implementation, each mobile terminal 54,56 isscheduled to be within the directional beam 52 for a respective timeinterval. During the time interval in which the directional beam 52 isdirected at the target mobile terminal 54, pilot and signalling channelscan be received at the terminal 54 along with the data traffic channels.During each of the other time intervals during which the beam isdirected towards the other mobile terminals 56, pilot and signallingchannels can be received at the corresponding terminals. Thedetermination of these transmission time intervals depends upon the datatransfer rate required by the target mobile terminal 54 and theacceptable time delays between receiving pilot and signalling channelinformation at the other mobile terminals 56. Hence, the setting of thetime intervals is an implementation detail which can be adjusteddepending upon the situation. In one alternative, rather than assigningmobile terminals respective time intervals, the rotating beam simplysweeps through the coverage area of the BTS 50 at a rate that enableseach mobile terminal to receive signalling and pilot channel burstswithin the time the beam is passing the particular mobile terminal. Inanother alternative, several of these beams may be active within asector. In this case, where the data traffic information also includesthe pilot signal and the pilot signal occupies the same frequency set asthe pilot signal of another beam, then techniques such as coding may beused at the transmit end and matched filtering at the receive end todifferentiate the two pilot signals belonging to the two beams.

FIGS. 2A and 2B illustrate two possible implementations for the BTS 50of the first embodiment of the present invention described above withreference to FIG. 1. In both the implementations of FIGS. 2A and 2B, theBTS 50 comprises a data information processor 60, a signallinginformation processor 62, a pilot processor 64, an Inverse Fast FourierTransform (IFFT) block 66 coupled to each of the processors 60,62,64 andan output block coupled to the IFFT block 66. These components functiontogether to process and transmit the data, signalling and pilot channelsto the appropriate mobile terminals 54,56. The difference between theseimplementations is the design of the output block and therefore, themanner in which the directional beam is generated. It is noted thatthere are other designs possible to generate a similar directional beam.

In both FIGS. 2A and 2B, the data information processor 60 is input withdata information and performs numerous well-known processing functionson the received data information; these well-known processing functionsincluding Forward Error Correction (FEC) encoding, rate matching,interleaving and modulation mapping. Although all of these functions areshown in a particular order in FIGS. 2A and 2B, one skilled in the artwould understand that these functions could be performed in a differentorder with a similar resulting output. Further, in alternativeembodiments, not all of the functions illustrated, such as FEC encoding,are performed by the processor 60 and/or additional functions notdescribed are also performed. It is noted that the data informationbeing input to the data information processor 60 could be in a number ofdifferent formats such as an Internet Protocol (IP) packet format,Motion Picture Experts Group (MPEG) coded images, video or anotherstandard data unit format.

The signalling information processor 62 is input with signallinginformation that needs to be transmitted to one or more of the mobileterminals within the coverage area. This processor 62 performswell-known processing functions similar to the data informationprocessor 60. These well-known processing functions in FIGS. 2A and 2Binclude FEC encoding, rate matching, interleaving and modulationmapping. It should be understood, similar to that described above forthe data information processor 60, that the signalling informationprocessor 62 could perform the functions in a different order thanillustrated in FIGS. 2A and 2B, might not perform all of these functionsand/or could perform additional functions not described.

The pilot processor 64, as illustrated in FIGS. 2A and 2B, is primarilyused to perform modulation mapping on pilot signals that are input tothe processor 64. Although not shown, it should be understood that thepilot processor 64 could perform additional functions not described.

Although illustrated and described as three separate and distinctprocessors 60,62,64, it should be understood that the common algorithmsperformed within these processors could be shared. Further, theseprocessors 60,62,64 could be implemented within a single component orwithin a plurality of separate components.

The IFFT block 66, illustrated within FIGS. 2A and 2B, operates totransform the frequency-based data, signalling and pilot signalsreceived from the data information processor 60, signalling informationprocessor 62 and the pilot processor 64 respectively into a time-basedoutput. This time-based output combines a data sub-carrier timesequence, a signalling sub-carrier time sequence and a pilot sub-carriertime sequence which is forwarded to the output block.

For the implementation illustrated within FIG. 2A, the BTS 50 includesan output block 70 that comprises a Peak to Average Power Ratio (PAPR)block 71 coupled to the IFFT block 66 and further coupled to a pluralityof parallel output paths; the PAPR block 71 reducing the peak to averagepower ratio of the signals forwarded to the output paths. Each of theoutput paths comprises a respective phase adjuster 72 a,72 b,72 c,72 dcoupled to the PAPR block 71 and further coupled in series with arespective outputting apparatus 74 a,74 b,74 c,74 d and a respectiveantenna 76 a,76 b,76 c,76 d; the antennas providing sector coverage. Inthis implementation, the phase by which each of the phase adjusters 72a,72 b,72 c,72 d adjusts the sub-carrier time sequences dictates theparticular direction the array of antennas' transmits the strongestenergy. Hence, to generate the rotating directional beam as describedabove for the first implementation of FIG. 1, the phase adjusters 72a,72 b,72 c,72 d are adjusted systematically such that the transmissionenergy is directed to each mobile terminal within the coverage area forthe proper time period.

In order to control the phase adjusters 72 a,72 b,72 c,72 d, the outputblock 70 further comprises a beam direction control block 78, coupled toeach of the phase adjusters, that is preferably implemented within anexisting processor of the BTS 50. Alternatively, the beam directioncontrol block 78 could be implemented within a separate processor or inhard logic devices. The beam direction control block 78 calculates thenecessary phase adjustments to direct the beam as required. In the caseof a BTS 50 that generates a rotating directional beam as illustrated inFIG. 2A, the block 78 continuously adjusts the phases of the differentoutput paths so that the resulting directional beam sweeps through thesector at the appropriate rate. In order to properly direct thedirectional beam, the beam direction control block 78 preferably isaware of the location of the mobile terminal(s) within the coveragearea; the block 78 determining the location of the mobile terminal(s)within its coverage area via a number of possible techniques. For one,in the case of fixed terminals, the block 78 could have the locations ofthe terminals within its coverage area predefined. Further, the mobileterminal(s) could report their location to the BTS 50 with the use of anon-board Global Positioning Satellite (GPS) apparatus (or similarlocation identifying apparatus). Yet further, the processing of signalsreceived from the mobile terminal(s) at the BTS 50 could allow the block78 to identify the location (or direction) of the mobile terminal(s);for example with the analysis of the angle of arrival of the mobileterminals' signals. In any of these cases, the determination of thelocation of the mobile terminal(s) within the coverage area allows thebeam direction control block 78 to set the phases of the phase adjusters72 a,72 b,72 c,72 d to point the beam in the desired direction.

As illustrated in FIG. 2A, the outputting apparatus 74 a,74 b,74 c,74 deach comprise a Digital-to-Analog (D/A) converter and a transmittercoupled in series between their respective phase adjusters 72 a,72 b,72c,72 d and their respective antennas 76 a,76 b,76 c,76 d. Theimplementation and operation of these components within the outputtingapparatus would be well-known by one skilled in the art.

For the implementation illustrated in FIG. 2B, the BTS 50 includes anoutput block 80 that comprises a PAPR block 81 coupled to the IFFT block66 and further coupled to a switch 82 and a plurality of output pathscoupled to the switch 82. The PAPR block 71 operates in a similar mannerto the PAPR block 61 described above. Each of the output paths comprisesa respective outputting apparatus 84 a,84 b,84 c,84 d coupled to theswitch 82 and further coupled in series with a respective directionalantenna 86 a,86 b,86 c,86 d. In this implementation, each of thedirectional antennas 86 a,86 b,86 c,86 d have a different principledirection for the strongest energy to be transmitted. Hence, to generatethe rotating directional beam, as described above for the firstembodiment of the present invention, the switch 82 systematicallyswitches the pilot, signalling and data sub-carrier time sequences todifferent outputting paths such that each mobile terminal within thecoverage area is being transmitted to during the proper time period. Asillustrated in FIG. 2B, the outputting apparatus 84 a,84 b,84 c,84 d areidentical to that described within the output block 70 illustratedwithin FIG. 2A.

Similar to FIG. 2A, the implementation of the BTS 50 of FIG. 2B furthercomprises a beam direction control block 88 that is coupled to theswitch 82. In this case, the beam direction control block operates tocontrol the switch 82 such that an appropriate directional antenna 86a,86 b,86 c,86 d is selected. Although not illustrated in all figuresshowing implementations for the BTS 50 depicted herein below, it shouldbe understood that at least one beam direction control block similar toblock 78 or block 88 would be implemented within each of theimplementations requiring one or more directional beams as describedherein below.

There are alternatives to the implementation of FIG. 2B. For instance,the switch 82 could be moved to reduce the need for multiple outputtingapparatus 84 a,84 b,84 c,84 d. In this alternative, the PAPR block 81could be implemented in series with a single outputting apparatus andthe switch 82, the switch 82 being coupled to each of the directionalantenna 86 a,86 b,86 c,86 d. This arrangement operates in a similarmanner as the implementation of FIG. 2B, but can reduce costs byreducing the need for additional D/A converters and transmitters. Theproblem with this alternative is that the switch 82 must be capable ofhandling high RF powers since it is located after the amplificationstage within the transmitter.

Although there are four parallel output paths with an antenna array offour within both the output block 70 of FIG. 2A and the output block 80within FIG. 2B, it should be recognized that other alternatives arepossible. In particular, it should be understood that additionalantennas could be included within the array, each additional antennahaving yet another parallel output path. If the output blockimplementation of FIG. 2A had greater than four output paths withcorresponding antennas, an increasingly focussed directional beam couldbe possible. If the output block implementation of FIG. 2B had greaterthan four output paths with corresponding antennas, each antenna couldbe designed to focus on a smaller slice of the overall coverage area,hence allowing for higher link gain. Similarly, it should be recognizedthat it is possible to implement the first implementation with less thanfour output paths with corresponding antennas.

FIG. 3 is a chart illustrating data, pilot and signalling sub-carrierfrequency allocations over time within an RF channel. Thisimplementation for an OFDM system is referred to as a “wandering”frequency allocation. In other implementations, the frequencyallocations can be fixed. Both wandering and fixed plot and signallingcarriers are used, for example, in the DVB-T transmission standard (seeETSI standard EN 300 744 V1.1.2 (1997-08) European Standard(Telecommunications series) Digital Video Broadcasting (DVB); framingstructure, channel coding and modulation for digital terrestrialtelevision). In either case, at any one time, each carrier is beingutilized by only one of the data, signalling and pilot channels. Hence,by separating out the carriers, it is possible to separate the data,signalling and pilot channels into a plurality of separatetransmissions. This is an important aspect of embodiments of the presentinvention described below with reference to FIGS. 4 to 9. If thewandering frequency allocation is used, it should be understood in thefollowing description that the apparatus is operated to take intoaccount the changing frequencies of the carriers for the data,signalling and pilots. These changes occur according to a pattern thatis known to both the transmitter and the receiver of the radio system.

These figures illustrate how the carriers fit together such that amobile terminal receiver may receive the signalling and pilot channels,the data channels, or both if the channels are transmitted throughantennas with differing coverage areas by the BTS 50.

In some embodiments of the present invention, a different antennaimplementation than is described above for the implementation of FIG. 1is utilized to ensure a sufficiently powerful transmission of the datachannels to the target mobile terminal while still maintainingtransmission of the pilot and signalling channels to any other mobileterminals within the coverage area. In these embodiments of the presentinvention, the RF channel is divided into at least two separatetransmissions, at least one for the data channels and at least one forthe pilot and signalling channels. One possible division of an RFchannel is illustrated within FIGS. 4A through 4C. FIG. 4A is a chartillustrating a sample OFDM signal in which pilot, signalling and datachannels are shown together. Here the pilot, signalling and datacarriers are shown with a similar legend as illustrated on FIG. 3. Asdepicted, these carriers are shown with differing amplitudes. Typically,the amplitude of each carrier would be chosen based upon the radiopropagation conditions and the modulation and coding being used. If thewandering pilot and signalling scheme were utilized, the frequencylocation of the channels would change with time. One of the datacarriers is shown with an increased amplitude to indicate, as notedpreviously, that the data channel may include pilot carriers to enablethe receiver to estimate the radio channel propagation conditions.

FIG. 4B is a chart illustrating the same sample OFDM signal of FIG. 4Awith the data channels removed, hence leaving only the signalling andpilot channels. FIG. 4C is a chart illustrating the same sample OFDMsignal of FIG. 4A with the pilot and signalling channels removed, henceleaving only the data channels.

Embodiments for transmitting the signal of FIG. 4C to the target mobileterminal while transmitting the signal of FIG. 4B to all of the mobileterminals within the coverage area will now be described with referenceto FIGS. 5 through 9. In these embodiments, there are only twotransmissions, though this should not limit the scope of the presentinvention. It should be recognized that expansions of these embodimentscould be designed in which the OFDM signals are divided into more thantwo transmissions. For instance, in one alternative embodiment, data,pilot and signalling channels could each have separate transmissions.

FIG. 5 is a block diagram illustrating a radio system using OFDM,according to a second embodiment of the present invention, similar tothat depicted in FIG. 1 but with the BTS 50 having a directionaltransmission beam for the data channels, hereinafter referred to as adata traffic directional beam, and a separate sector omni-directionaltransmission beam for the pilot and signalling channels, hereinafterreferred to as a service sector omni-directional beam. Within FIG. 5, adirectional beam 88 is utilized as the data traffic beam in order forthe BTS 50 to transmit the data traffic with sufficient link gain to thetarget mobile terminal 54 while a sector omni-directional beam 89 isutilized as the service beam in order for the BTS 50 to transmit thepilot and signalling channels continually to all of the mobile terminalsin its coverage area. A sector omni-directional beam is generallysufficient for transmission of the pilot and signalling channels to themobile terminals since the bit rate of these transmissions is generallylower compared with that for the data traffic channels.

To enable a sufficient link budget, the service sector omni-directionalbeam may have a different modulation or symbol rate compared to the datadirectional beam in order to compensate for the broader service beam. Inone implementation, the Hierarchical modulation technique used in theDVB-T standard as described previously is used for the service beam. Inthis case, the data directional beam is operated in the full modulationconstellation while the service sector omni-directional beam operates inthe smaller modulation constellation. One advantage of this technique isthat the same receiver can be used to receive both portions of the OFDMsignal.

FIGS. 6A, 6B and 6C are block diagrams illustrating first, second andthird possible implementations of the BTS 50 of the second embodiment ofthe invention. These possible implementations of the BTS 50 include anidentical data information processor 60, signalling informationprocessor 62, pilot processor 64 and IFFT block 66 as described abovefor FIGS. 2A and 2B. Similar to the BTS of FIGS. 2A and 2B, the blocks60,62,64,66 of FIGS. 6A,6B,6C could be implemented with alternativeversions as discussed above.

The difference between the BTS designs of FIGS. 2A, 2B, 6A, 6B and 6Care the different implementations of their respective output blocks.FIGS. 6A, 6B and 6C illustrate three possible implementations of outputblocks that allow for the generation of the transmission beams 88,89 ofFIG. 5 according to the second embodiment of the present invention. Thebelow description of these three implementations should not limit thescope of the present invention for it should be understood that thesesample implementations are not meant to be an inclusive set of allpossible implementations.

For the implementation illustrated within FIG. 6A, the BTS 50 includesan output block 90 that comprises a data traffic beam PAPR block 91coupled to the IFFT block 66 and further coupled to a plurality ofparallel data traffic beam output paths; and a service beam PAPR block97 coupled to the IFFT block 66 as well as a separate service beamoutput path. The operation of the PAPR blocks 91,97 are similar to thatdescribed above for block 71 with reference to FIG. 2A. As well, similarto that described above with FIG. 2A, each of the data traffic beamoutput paths comprises a respective phase adjuster 92 a,92 b,92 c,92 dcoupled to the PAPR block 91 and further coupled in series with arespective outputting apparatus 94 a,94 b,94 c,94 d and a respectiveantenna 96 a,96 b,96 c,96 d. In this implementation the antennas 96 a,96b,96 c,96 d are sector omni-directional antennas with the directionalbeam 88 being formed through the use of the phase adjusters. The phaseadjusters 92 a,92 b,92 c,92 d each receive the data trafficsub-carrier's time sequences from the PAPR block 91 and adjust the phaseof the sub-carrier time sequences in order to dictate the particulardirection the array of antennas' transmits the strongest energy. Hence,to generate the data traffic beam 88 as described above for the secondembodiment of the present invention, the phase adjusters 92 a,92 b,92c,92 d are adjusted such that the transmission energy is directed to thetarget mobile terminal. As discussed previously, a beam directioncontrol block similar to that described above for block 78 would befurther implemented to control the phase adjusters 92 a,92 b,92 c,92 d.

The service beam output path comprises an outputting apparatus 98coupled between the PAPR block 97 and a service beam antenna 99. In thisimplementation, the outputting apparatus 98 receives the pilot andsignalling data-carrier's time sequence from the PAPR block 97 and,after processing these time sequences, forwards them to the antenna 99.The antenna 99 is a sector omni-directional antenna that allows for thetransmission of the service beam 89 throughout the coverage area of theBTS 50 with relatively even link gain.

Similar to that described above for the output block of FIG. 2A, theoutputting apparatus 94 a,94 b,94 c,94 d,98 of FIG. 6A each comprise aD/A converter and a transmitter coupled to their respective antennas 96a,96 b,96 c,96 d,99. The implementation and operation of the componentswithin the outputting apparatus would be well-known by one skilled inthe art.

In the implementation of FIG. 6A, and in further implementationsdescribed herein, the IFFT block 66 provides two output time sequences,one for the service sub-carriers (pilot and signalling) and the otherfor the data traffic sub-carriers. These two time sequences may bereadily formed by the IFFT block 66 by performing two IFFT operations onthe two groups of sub-carriers. Alternatively, a single IFFT operationcould be performed but with a modified output calculation utilizing twooutput accumulators, each accumulator arranged to include onlycomponents of the corresponding sub-carriers.

For the implementation illustrated in FIG. 6B, the BTS 50 includes anoutput block 100 which is virtually identical to that described abovewith reference to FIG. 6A. The alternative that is being illustrated inFIG. 6B is the sharing of the service beam antenna with one of the datatraffic beam antenna. As depicted within FIG. 6B, an outputtingapparatus 102 is coupled to the PAPR 97 in order to receive a pilot andsignalling sub-carrier time sequence while the apparatus 102 is furthercoupled to the first data traffic phase adjuster 92 a in order toreceive phase adjusted data traffic sub-carrier time sequences. As shownin FIG. 6B, the outputting apparatus 102 is yet further coupled to anantenna 104. Similar to the outputting apparatus of FIG. 6A, theoutputting apparatus 102 comprises a D/A converter and a transmitter.

The sharing of the antenna 104 is possible because, as discussed above,the pilot and signalling sub-carriers and the data traffic sub-carriersoperate with different carriers. With this implementation, the phaseadjusted data carriers transmitted from the sector omni-directionalantenna 104 work in unison with the phase adjusted data carriertransmissions from the other data traffic sector omni-directionalantenna 96 b,96 c,96 d to generate a directional data traffic beam. Theshared antenna 104 also generates a sector omni-directional service beamdue to the pilot and signalling sub-carriers being transmitted on theomni-directional antenna. In this implementation, as well as otherimplementations described herein below in which an outputting apparatusreceives two input time sequences, the outputting apparatus can readilycombine the two time sequences into a single stream by adding togetherthe time coincident pairs of the two time sequences. In this case, therelevant PAPR blocks must include the additional summation indetermining their compensation to limit the peak power.

Now turning to the alternative implementation depicted within FIG. 6C,the BTS 50 includes an output block 110 that comprises a PAPR 91, aswitch 112 and a plurality of data traffic beam output paths similar tothat depicted within FIG. 2B while also comprising a PAPR block 97 and aservice beam output path similar to that depicted within FIG. 6A. Eachof the data traffic beam output paths comprises a respective outputtingapparatus 114 a,114 b,114 c,114 d coupled to the switch 112 and furthercoupled in series with a respective directional antenna 116 a,116 b,116c,116 d. Similar to that described above for FIG. 2B, each of thedirectional antennas 116 a,116 b,116 c,116 d have a different principledirection for the strongest energy to be transmitted. Hence, to generatethe data traffic directional beam the switch 112 switches the datasub-carrier time sequences to a different data traffic beam output pathso that the target mobile terminal is being transmitted to with asufficient link gain. Similar to that described with reference to FIG.6A, the service beam output path comprises an outputting apparatus 98coupled between the PAPR block 97 and a sector omni-directional antenna99. As described previously, the outputting apparatus 98 receives apilot and signalling sub-carrier time sequence from the PAPR block 97and, after processing this time sequence, forwards it to the antenna 99.The antenna 99 is a sector omni-directional antenna that allows for thetransmission of the service beam throughout the coverage area of the BTS50 with relatively even power. As illustrated in FIG. 6C, the outputtingapparatus 114 a,114 b,114 c,114 d,98 are identical to those describedpreviously with reference to FIGS. 2A, 2B, 6A and 6B.

As discussed with reference to FIG. 2B, an alternative implementationwith a single data traffic beam outputting apparatus is possible byhaving the switch 112 located between the single data traffic beamoutputting apparatus and the plurality of directional antennas 116 a,116b,116 c,116 d. In this case, as discussed previously, the switch must besufficient to handle signals of relatively high power in thisimplementation.

Similar to that described above for the first embodiment, the secondembodiment of the present invention should not be limited to having fourparallel data traffic beam output paths with an antenna array of fourwithin the output block. In particular, it should be understood thatadditional antennas could be included within the array, each additionalantenna having yet another parallel data traffic beam output path. Ifthe output block implementation of FIG. 6A or 6B had greater than fourdata traffic beam output paths with corresponding antennas, anincreasingly focussed directional beam could be possible. If the outputblock implementation of FIG. 6C had greater than four data traffic beamoutput paths with corresponding antennas, each antenna could be designedto focus on a smaller slice of the overall coverage area, hence allowingfor greater link gain. Similarly, it should be recognized that it ispossible to implement the present invention with less than four outputpaths with corresponding antennas.

In another alternative implementation of the second embodiment of thepresent invention, the sector omni-directional beam 89 could be replacedwith a plurality of partial sector omni-directional beams, each of thepartial sector omni-directional beams covering a subset of the overallcoverage area. In this case, additional antennas would be required tocover the entire the coverage area. One advantage of this alternative isthe increased power that is possible for transmitting the pilot andsignalling channels if the sector omni-directional beam is divided intoa plurality of more narrowly focussed beams.

FIG. 7 is a block diagram illustrating a radio system using OFDM,according to a third embodiment of the present invention, similar tothat depicted in FIG. 5 but with the BTS 50 having a data trafficdirectional beam 118 and a separate service directional beam 119. WithinFIG. 7, the data traffic directional beam 118 allows the BTS 50 totransmit the data traffic with sufficient link gain to the target mobileterminal 54 similar to that described for FIG. 6A while the servicedirectional beam 119 allows the BTS 50 to transmit the pilot andsignalling channels to all of the mobile terminals in its coverage area.This alternative is particularly advantageous in cases where the linkgain of a sector omni-directional beam is not sufficient fortransmission of the pilot and/or signalling channels to the mobileterminals. The directional service beam can be swept about the coveragearea to reach all of the mobile terminals in time. Additionally, aplurality of service beams 118 could be used to reach a plurality ofmobile terminals simultaneously. The service beam may also be directedto a target mobile terminal for transmission of specialized signallingmessages.

FIGS. 8A, 8B and 8C are block diagrams illustrating first, second andthird possible implementations of the BTS 50 of the third embodiment ofthe invention. These possible implementations of the BTS 50 include anidentical data information processor 60, signalling informationprocessor 62, pilot processor 64 and IFFT block 66 as described abovefor FIGS. 2A, 2B, 6A, 6B and 6C. Similar to the BTS of the previousfigures, the blocks 60,62,64,66 of FIGS. 8A,8B,8C could be implementedwith alternative versions as discussed above.

The difference between the BTS designs of FIGS. 2A,2B,6A,6B,6C,8A,8B and8C are the different implementations of their respective output blocks.FIGS. 8A, 8B and 8C illustrate three possible implementations of outputblocks that allow for the generation of the transmission beams 118,119of FIG. 7 according to the third embodiment of the present invention.The below description of these three implementations should not limitthe scope of the present invention for it should be understood thatthese sample implementations are not meant to be an inclusive set of allpossible implementations.

For the implementation illustrated within FIG. 8A, the BTS 50 includesan output block 120 that comprises a data traffic beam PAPR 91 and aservice beam PAPR block 121 as described previously as well as aplurality of parallel output paths that are shared between the datatraffic directional beam transmission and the rotating servicedirectional beam transmission. As depicted within FIG. 8A, each of theoutput paths comprise a respective outputting apparatus 124 a,124 b,124c,124 d; a respective data traffic beam phase adjuster 92 a,92 b,92 c,92d coupled between the data traffic beam PAPR block 91 and the respectiveoutputting apparatus 124 a,124 b,124 c,124 d; a respective service beamphase adjuster 122 a,122 b,122 c,122 d coupled between the service beamPAPR block 121 and the respective outputting apparatus 124 a,124 b,124c,124 d; and a respective sector omni-directional antenna 126 a,126b,126 c,126 d. These sector omni-directional antennas are directed toform the beams by means of the phase adjusters that are controlled byrespective beam direction control blocks (not shown) similar to theblock 78 described previously with reference to FIG. 2A.

In this implementation, the data traffic beam phase adjusters 92 a,92b,92 c,92 d each receive a data traffic sub-carrier time sequence fromthe PAPR block 91 and adjust the phase of the sub-carrier time sequencein order to dictate the particular direction the array of antennas'transmits the data channels with the greatest link gain. Hence, togenerate the data traffic beam 118 as described above for the thirdembodiment of the present invention, the phase adjusters 92 a,92 b,92c,92 d are adjusted such that the transmission energy is directed to thetarget mobile terminal. On the other hand, the service beam phaseadjusters 122 a,122 b,122 c,122 d each receive a service sub-carriertime sequence from the PAPR block 121 and adjust the phase of theservice beam sub-carrier time sequence to dictate the particulardirection the array of antennas' transmits the pilot and signallingchannels with the greatest link gain. Hence, to generate the servicedirectional beam 119 as described above for the third embodiment of thepresent invention, the service beam phase adjusters 122 a,122 b,122c,122 d are adjusted systematically such that the transmission energy isdirected to all areas within the coverage area for the proper timeperiod.

Similar to that described above for other output blocks, the outputtingapparatus 124 a,124 b,124 c,124 d of FIG. 8A each comprise a D/Aconverter and a transmitter coupled to their respective antennas 126a,126 b,126 c,126 d. The implementation and operation of the componentswithin the outputting apparatus would be well-known by one skilled inthe art.

For the implementation illustrated in FIG. 8B, the BTS 50 includes anoutput block 130 which is virtually identical to that described abovewith reference to FIG. 8A, but with separate output paths for the datatraffic and service beams. As depicted within FIG. 8B, the output block130 comprises the PAPR blocks 91,121 and four parallel data traffic beamoutput paths identical to those illustrated in FIG. 6A along with fourparallel service beam output paths. Each of the data traffic beam outputpaths comprises a respective data traffic beam phase adjuster 92 a,92b,92 c,92 d coupled to the data traffic beam PAPR block 91 and furthercoupled in series with a respective outputting apparatus 94 a,94 b,94c,94 d and a respective sector omni-directional antenna 96 a,96 b,96c,96 d. On the other hand, each of the service beam output pathscomprises a respective service beam phase adjuster 122 a,122 b,122 c,122d coupled to the service beam PAPR block 121 and further coupled inseries with a respective outputting apparatus 134 a,134 b,134 c,134 dand a respective sector omni-directional antenna 136 a,136 b,136 c,136d. In this implementation, the data traffic beam phase adjusters 92 a,92b,92 c,92 d each receive a data traffic sub-carrier time sequence fromthe data traffic beam PAPR block 91 and adjust the phase of thesub-carrier time sequence in order to dictate the particular directionthe array of antennas' transmits the data channels with the greatestlink gain. On the other hand, the phase by which each of the servicebeam phase adjusters 122 a,122 b,122 c,122 d adjusts the service beamsub-carrier time sequence dictates the particular direction the array ofantennas' transmits the pilot and signalling channels with the greatestlink gain. The eight parallel output paths within FIG. 8B operatetogether to generate the data traffic and service beams 118,119 similarto those generated by the output block 120 of FIG. 8A.

Now turning to the alternative implementation depicted within FIG. 8C,the BTS 50 includes an output block 140 that comprises the data trafficbeam PAPR block 91 coupled to the IFFT block 66; a data traffic beamswitch 141 coupled to the data traffic beam PAPR block 91; a servicebeam PAPR block 121 coupled to the IFFT block 66; a service beam switch142 coupled to the service beam PAPR block 121; and a plurality ofoutput paths similar to that depicted within FIG. 2B coupled to both ofthe switches 141,142. Each of the output paths comprises a respectiveoutputting apparatus 144 a,144 b,144 c,144 d independently coupled toeach of the switches 141,142 and further coupled in series with arespective directional antenna 146 a,146 b,146 c,146 d. Similar to thatdescribed above for FIG. 2B, each of the directional antennas 146 a,146b,146 c,146 d have a different principle direction for the strongestenergy to be transmitted. Hence, to generate the data trafficdirectional beam 118 the switch 141 switches the data sub-carrier timesequences to a different output path so that the target mobile terminalis being transmitted to with sufficient link gain. To generate therotating service directional beam 119, as described above for the thirdembodiment of the present invention, the switch 142 systematicallyswitches the pilot and signalling sub-carrier time sequences todifferent outputting paths such that each mobile terminal within thecoverage area is being transmitted to during the proper time period. Asillustrated in FIG. 8C, the outputting apparatus 144 a,144 b,144 c,144 dare identical to those described previously.

The above description with reference to FIG. 8C is applicable to a casethat can utilize low power switches. A similar alternative to thatdescribed previously can apply to this embodiment with the switches141,142 located between a single outputting apparatus and the pluralityof antennas. In this case, the switches would need to be extremely highpower which might make this alternative impractical with currenttechnology.

Similar to that described above for the first and second embodiments,the third embodiment of the present invention should not be limited tohaving four parallel data traffic and service beam output paths with anantenna array of four within the output block. It should be understood,similar to the embodiments described above, more or less than fouroutput paths could be used in implementations according to the thirdembodiment of the present invention. Further, although not illustratedin the attached figures other alternatives could be made to theimplementations illustrated in FIGS. 8A,8B and 8C. For instance, theembodiment of FIG. 8C could be implemented with separate output pathsfor the data traffic and service beams. This would be a similaralternative to the implementation of FIG. 8B compared to theimplementation of FIG. 8A.

Although depicted as beams of similar focus on FIG. 7, it should berecognized that the rotating service directional beam could be broaderthan the data directional beam. For radio systems in which the receivermust estimate the channel propagation conditions, it is mostadvantageous for the two beams to be of the same pattern so that thepilot signals received from the service beam transmission closely matchthose of the data traffic beam.

To enable a sufficient link budget, the rotating service directionalbeam may have a different modulation or symbol rate compared to the datadirectional beam in order to compensate for a broader beam. In oneparticular implementation, the hierarchical modulation technique used inthe DVB-T standard as described herein above is used for the rotatingservice directional beam. In this case, the data directional beam isoperated in the full modulation constellation while the rotating servicedirectional beam operates in the smaller modulation constellation. Oneadvantage of this technique is that the same receiver can be used toreceive both portions of the OFDM signals.

FIG. 9 is a block diagram illustrating a radio system using OFDM inwhich two adjacent sectors each have a rotating directional beam. Asdepicted, first and second cells 150,160 comprise respective BTS 152,154which transmit OFDM signals within sector N 154 and sector M 164respectively. Within these sectors 154,164, the BTS 152,162 transmitrespective rotating directional beams 156,166. This could occur in anyone of the implementations of the embodiments of the invention in whicha rotating directional beam is utilized. In this case, one area ofconcern is the possibility that both rotating directional beams couldoverlap at a particular mobile terminal, mobile terminal 158 within FIG.9 for example. If the sub-carriers within the rotating directional beams156,166 are utilizing common carriers this could cause significantinterference at the mobile terminal. To avoid this problem, the rotatingdirectional beams 156,166 can be timed such that they are not bothfocussed on the same mobile terminal at the same time. As well, to avoidpossible interference, techniques such as coding or other interferencecancellation techniques could be utilized to enable the receiver todifferentiate the transmissions (data, pilot, signalling) from the twoor more beams. This allows for acceptable frequency re-use while notincreasing frequency interference between cells significantly.

FIG. 10 is a block diagram of a mobile terminal that could be utilizedwithin the OFDM systems illustrated in any one of FIGS. 1, 5 and 7. Asdepicted, the mobile terminal comprises an antenna 170 coupled in serieswith a receiver 172, a frequency offset correction block 174, a pilotsub-carrier acquisition block 176, a Fast Fourier Transform (FFT) block178 and a demulitplexer 180. In this implementation, the demultiplexer180 is further independently coupled to a data information processor 182and a service information processor 184. These components functiontogether to receive and process the data, signalling and pilot channelssent from the BTS 50. In FIG. 10, the antenna 170, the receiver 172, thefrequency offset correction block 174 and the pilot sub-carrieracquisition block 176 are utilized to initially receive and synchronizethe signals sent for the BTS 50. Next, the FFT block 178 operates totransform the time-based data, signalling and pilot signals receivedfrom the pilot sub-carrier acquisition block 176 into frequency-basedoutput symbol streams. These frequency-based output symbol streamsinclude a data sub-carrier symbol stream, a signalling sub-carriersymbol stream and a pilot sub-carrier symbol stream which are eachforwarded to the demultiplexer 180. The demultiplexer 180 separates thesymbol streams such that the data sub-carrier symbol stream is forwardedto the data information processor 182 while the signalling and pilotsub-carrier symbol streams are forwarded to the service informationprocessor 184.

The data information processor 182 performs numerous well-knownprocessing functions on the received data sub-carrier symbol stream inorder to output data information contained within the input signals.These well-known processing functions include symbol demodulation, datade-interleaving, rate matching and FEC decoding. Although all of thesefunctions are shown in a particular order in FIG. 10, this should notlimit the scope of the present invention. One skilled in the art wouldunderstand that these functions could be performed in a different orderwith a similar resulting output. Further, in alternative embodiments,not all of the functions illustrated, such as FEC decoding, areperformed by the processor 182 and/or additional functions not describedare also performed. It is noted that the data information being outputfrom the data information processor 182 could be in a number ofdifferent formats such as an Internet Protocol (IP) packet format, MPEGcoded images, video or another standard data unit format.

The service information processor 184 performs well-known processingfunctions similar to the data information processor 182. Thesewell-known processing functions in FIG. 10 include symbol demodulation,signalling de-interleaving, rate matching and FEC decoding. It should beunderstood, similar to that described above for the data informationprocessor 182, that the service information processor 184 could performthe functions in a different order than illustrated in FIG. 10, mightnot perform all of these functions and/or could perform additionalfunctions not described. Yet further, it should be understood that theservice information processor could be divided into at least twoprocessors, one for processing the signalling sub-carrier symbol streamand one for processing the pilot sub-carrier symbol stream. If two ormore pilot signals using the same frequency carriers are received at thetarget mobile terminal, techniques such as matched filtering orcorrelation may be used to select the desired signal.

Although illustrated and described as two separate and distinctprocessors 182,184, it should be understood that the common algorithmsperformed within these processors could be shared. Further, theseprocessors 182,184 could be implemented within a single component orwithin a plurality of separate components.

There is a modification from traditional mobile terminals that would beimplemented within preferable implementations of the mobile terminals ofthe present invention. In preferable implementations of the mobileterminals of the present invention, a monitor device (not shown),coupled to the outputs of the data information processor 182 and theservice information processor 184, determines what information is beingreceived at the mobile terminal at any particular time. This monitordetermines if only service information is being received, thusindicating that the particular mobile terminal is outside the datatraffic beam but within the service beam; if only data trafficinformation is being received, thus indicating that the particularmobile terminal is inside the data traffic beam but outside the servicebeam; and if both data traffic information and service information isbeing received, thus indicating that the particular mobile terminal isinside both the data traffic and service beams. The monitor, afterdetermining what information is being received at the mobile terminal,in this particular implementation, then directs the processing of thereceived data traffic and service information as required.

It should be noted that although the mobile terminal is illustrated in asingle receiver structure within FIG. 10, it should be recognized thatit could be possible to implement the terminal with separate receiverstructures for the data traffic beam and the service beam. Thistechnique would have the additional disadvantages of significantlyadditional costs due to additional components.

One modification that is required within some embodiments of the presentinvention is the introduction of pilot carriers within a data trafficbeam as described previously. If precise channel estimations arerequired for the data channels, a separate data beam pilot signal isrequired since the transmission of the standard pilot signals via theservice beam may not be accurate for the data traffic beam. In oneparticularly preferable embodiment of the present invention, the pilotsignals within the standard pilot channels of the service beam areutilized by the target mobile terminal to generate a broad estimationand synchronization while the data traffic pilots within the datatraffic beam are utilized by the target mobile terminal to focus in onthe synchronization of the data traffic channels and to estimate theradio propagation conditions.

Although not specifically described above it should be noted that thepresent invention can apply in cases of mobile terminals within an OFDMcell as well as fixed wireless terminals within an OFDM cell. In thecase of a fixed access system in which the subscriber terminals are in arelatively fixed locations, such as inside a residence, the beamdirection can be fixed for each subscriber. In this case, thedirectional beam can be steered towards each subscriber with use of atable of steering values applicable for each subscriber.

Further, although not discussed above, it should be understood that thepresent invention could be combined with interference cancellationtechniques in order to suppress interference between cells on theservice beam. That is the mobile terminal, knowing the transmissioncharacteristics of all of the pilots in the area may cancel out thosethat are interfering with the primary signal. It is also possible tosynchronize the service beam (i.e. the timing of their use within thesectors) to minimize the interference between cells to enable efficientfrequency reuse.

Yet further, although the embodiments of the present invention werespecifically described above for a system in which the BTS transmits adata traffic beam and a service beam to the mobile terminals, it shouldbe recognized that there could be alternative divisions of thetransmission beams. For instance, either one of the service and datatraffic beams could be subdivided into additional beams. For example,the data traffic beam could be divided between audio traffic andtraditional data traffic or could be divided between audio and videotraffic. As discussed previously, one possible division of the servicebeam is to divide the pilot channels and the signalling channels intoseparate beams. Additionally, the signalling channels could be furthersubdivided.

Although the present invention has been described herein abovespecifically for OFDM systems, it should be recognized that direct radioenergy (beam) systems that might be developed in the future that havesimilar characteristics might also benefit from the implementation ofthe present invention.

Persons skilled in the art will appreciate that there are yet morealternative implementations and modifications possible for implementingthe present invention, and that the above implementations are onlyillustrations of certain embodiments of the invention. The scope of theinvention, therefore, is only to be limited by the claims appendedhereto.

1. A Base Transceiver Station (BTS) arranged to communicate with aplurality of mobile terminals within a coverage area, the BTScomprising: means for receiving service and data traffic information;means for transmitting the service information on a first set ofcarriers to the mobile terminals within the coverage area; and means fortransmitting the data traffic information with high link gain on asecond set of carriers to the target mobile terminal.
 2. A method oftransmitting service and data traffic information to a plurality ofmobile terminals within a coverage area, at least one of the mobileterminals being a target mobile terminal, the method comprising:receiving service and data traffic information; transmitting the serviceinformation on a first set of carriers to the mobile terminals withinthe coverage area using a first transmission beam; and transmitting thedata traffic information on a second set of carriers to the targetmobile terminal using a second transmission beam.
 3. A method oftransmitting service and data traffic information to a plurality ofmobile terminals within a coverage area, at least one of the mobileterminals being a target mobile terminal, the method comprising:receiving service and data traffic information; transmitting the serviceinformation on a first set of carriers to the mobile terminals withinthe coverage area with a directional transmission beam; transmitting thedata traffic information on a second set of carriers to the targetmobile terminal with the directional transmission beam; and modifyingthe direction of focus of the directional transmission beam in order foreach of the mobile terminals within the coverage area to receive theprocessed service information.
 4. A mobile terminal arranged tocommunicate with a Base Transceiver Station (BTS), the mobile terminalcomprising: a radio reception apparatus that operates to receive andprocess service information on a first set of carriers from at least onefirst transmission beam and to receive and process data trafficinformation on a second set of carriers from at least one secondtransmission beam; and a monitor apparatus, coupled to the radioreception apparatus, that operates to determine if one or more ofservice information and data traffic information has been received atthe radio reception apparatus; if only service information has beenreceived, to instruct the BTS to attend to the received serviceinformation; if only data traffic information has been received, toinstruct the BTS to attend to the received data traffic information; andif service and data traffic information has been received, to instructthe BTS to attend to both the received service and data trafficinformation.